1. Field of the Invention
The present invention relates to an anti-skid apparatus for installation in a vehicle braking system to prevent the road wheels of the vehicle from locking in braking operation.
2. Description of the Prior Art
In this kind of technical field, there has been proposed an anti-skid apparatus of the type which includes speed detecting means arranged to detect each rotational speed of road wheels of the vehicle for producing electric signals respectively indicative of the detected wheel speed, an electrically operated actuator arranged to control hydraulic brake pressure applied to each wheel brake cylinder of the road wheels, and an electronic control device for applying an electric control signal to the actuator in response to the electric signals from the speed detecting means so that the actuator is operated to control the brake pressure in accordance with road surface conditions. The operation of the actuator is conducted under control of the electronic control device when the wheel speed in braking operation becomes lower than a reference speed the value of which is defined by a multiplied value of the wheel speed with a predetermined slip ratio and also the negative acceleration of the road wheels becomes smaller than a predetermined value. Disclosed in Japanese Patent Publication No. 58-58254 is an anti-skid apparatus designed to prevent erroneous operation of the actuator during travel of the vehicle on a rough road such as a gravel road, a rugged road or the like.
During travel of the vehicle equipped with the conventional anti-skid apparatus, the rotational speed of the respective road wheels does not decrease lower than the reference speed even when the vehicle is braked by light depression of the brake pedal on a flat road. If in such braking operation there are steps on the travel road, the road wheels of the vehicle are floated in a moment from the travel road to cause sudden decrease of the torque acting on the wheel tires. In this instance, the rotational speed of the respective road wheels becomes lower than the reference speed, and the negative acceleration of the road wheels becomes smaller than the predetermined value. As a result, the actuator is operated to decrease the brake pressure applied to the wheel brake cylinders. Accordingly, the road wheels of the vehicle may not be applied with sufficient braking force even when grounded after passing over the steps on the travel road, and the driver is applied with unpleasant feel since the actuator is operated by light depression of the brake pedal.